I have just moved to Seabrook, Texas a few months ago and my front garden has two lovely gardenia bushes. One started to have some yellow leaves and now the other one has them as well. I don't want to lose them but don't know how to make them healthy.
Check out which leaves are turning yellow. If young leaves near the tips are yellowing while older leaves remain green, your plant is exhibiting iron deficiency. If older leaves are the ones yellowing and dropping, the problem may be soggy growing conditions which can destroy roots by cutting off their supply of oxygen. Nitrogen deficiency shows up as yellowing of older leaves first and in time can progress to all the leaves on a plant.
Other causes of yellow, dropping leaves are drought, certain types of herbicide injury, and physical damage to plant roots.